I thought about building an Opentherm gateway at first but then I realized that it might worth to add some more functionality (by incorporating a temperature sensor and some logic) to act like a standalone thermostat, too.

That's it, by reading the boiler parameters (in gateway mode), I could make use of instant flow/return temperatures and by logging the room temperature versus time (and setpoint / modulation level) I could compute a heating/coo!ing curve for my house.

I want to use an Arduino and a ESP8266 wifi board to get wireless functionality. I could further add various RF sensor nodes for outside and zone temp sensors.

Does anyone built/start such a project, to not reinvent the wheel? I've read and searched a lot but I didn't found anything.